Fibrous insulating materials and channels lined with same



M. D. ASH

Filed March 23, 1966 Nov. 25, 1969 F/GZ United States Patent 3,480,125 FIBROUS INSULATING MATERIALS AND CHANNELS LINED WITH SAME Malcolm Donald Ash, Wirral, England, assignor to Morgan Refractories Limited, Wirral, England, a British company Filed Mar. 23, 1966, Ser. No. 536,826 Claims priority, application Great Britain, Mar. 26, 1965, 12,962/ 65 Int. Cl. B65g 7l/16; B32b 7/14; D04h 1/30 U.S. Cl. 193-2 6 Claims ABSTRACT F THE DISCLOSURE A ceramic blanket, particularly suitable for lining apparatus handling molten metals, comprises a thickness of felted or matted ceramic fibres of alumina and silica stiffened by treatment with a silica sol from one surface part way only through its thickness towards the other surface. In this way part of the thickness is rigid enough to keep its shape but the remainder is resilient and resists shocks.

This invention comprises improvements in or relating to fibrous insulating materials.

It is known to produce a thermal insulating material in the form of a blanket of felted heat-resisting fibres, for instance asbestos fibres, or glass fibres, or fibres formed from a melt of a mineral, or mineral mixture, containing alumina and silica. One manner of manufacturing such thermal insulating material is described in U.S. patent specification No. 3,023,141.

Such blankets as have been manufactured hitherto are flexible and this gives rise to diiiiculties or disadvantages in some applications. Therefore, for some purposes the blanket is preformed to a desired shape but in so doing the blanket may be so stilfened to avoid loss of shape in handling, that the heat-insulating properties are irnpaired, or that desirable resilience and compressibility of the surfaces are reduced to a large extent.

This invention provides improved means of stiffening heat insulation, such as a blanket, comprising a felted or matted layer of libres which are formed from a mineral, or mixture of minerals, containing alumina and silica, which means comprises applying a silica sol to one surface of the layer, the other surface being untreated.

It is found that the heat insulation so treated can be stiftened only part way through its thickness and can retain a desired shape wit-hout a large reduction in the heat-insulating characteristicts occurring and Without substantial loss of the resilience and compressibility of the said other surface.

The fibrous layer may be stiffened by applying the silica sol to one surface, as by spraying, brushing, or dipping, in such a regulated manner that the sol does not penetrate through the thickness of the layer and by then heating to dry out the layer. It has been found that if the quantity of sol applied per unit area is suitably regulated in relation to the thickness of the libre layer, and its density, the silica sol does not spread through the thickness of the layer. The sol tends to be retained towards the surface on which it is applied and penetrates further through the thickness of the layer as additional quantities are applied and it is readily possible by trial to determine the `quantity of a particular sol which must be used to obtain a particular penetration with a particular type of fibrous layer. The penetration is roughly proportional to the dosage per unit area, and the dosage per unit area to achieve penetration through a given proportion of the thickness varies as the thickness.

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The stiffness of the stiffened layer may be varied, for a given rate of application of sol, by varying the quantity of solids in the sol; the greater the quantity of solids per unit volume of sol, the greater will be the stiffness imparted to the fibre layer.

The libre layer, say in the form of a blanket, may be cut to a desired shape before or after the stiffening process, and may be stiffened while supported on a former so as to have a desired final contour.

The libres forming the layer should have an alumina content of at least 40% by weight, and, excluding impurities, the composition of the libres is suitably 40% to 60% by weight of alumina and 60% to 40% silica. A particular form of libre has a composition consisting of between 43% and 48% alumina, between 55% and 49% silica, and between 2% and 3% impurities. Such a fibre might be prepared from clay by any known or convenient fibre-forming process. The fibres in the layer conveniently have an average ratio of their lengths to their diameters of at least 100,000 to 1.

The silica sol employed can have a wide content range of solids. For instance good results are obtained using sols containing 'between 5% to 35% by weight of solids. Normally for ease of handling a sol having a solids content of between 9% and 21%, and preferably 9% to 11%, will be used.

The accompanying drawings illustrate by way of example a method and product of the invention and one use for the product.

In the drawings:

FIG. 1 shows a blanket of ceramic fibres being treated, and

FIG. 2 shows the use of a treated layer of ceramic fibres as a lining for a molten metal launder.

The drawings are hereinafter referred to.

The following examples illustrate the invention.

EXAMPLE I A ceramic fibre blanket 10 (FIG. 1), whereof the fibres consist of alumina and silica and which has a density of 8 lbs. per cubic foot, is treated as indicated on one surface thereof 4by applying with a brush 12 a 30% solids silica sol at the rate of 1%. pints per square foot per inch thickness of the blanket. The blanket is then dried and a product is obtained which is suiiiciently stiff to be handled but which ha-s a resilient surface so that the blanket has a significant degree of compressibility. Examination shows that the sol penetrates through about half the thickness of the blanket as indicated by the additional horizontal hatching 11.

A dosage of 3 pints per square foot per inch thickness resulted in a completely rigid product, the sol having penetrated the full thickness.

EXAMPLE II A blanket as used in Example I is treated -with a 10% solids silica sol vat the rate of 11/2 pints per square foot per inch thickness. After dying, the product is capable of being handled without losing its shape, but has a greater resilience than the product of Example I. Equal results are obtained by brushing on the sol, or yby spraying on, or by dipping the blanket into a tray containing a mea-sured quantity of the sol.

The drying temperature is not critical but should be above 30 C., for instance 50 C.

The material may be tested for strength for example by supporting test pieces 8 cms. long x l cm. wide x 1.25 cms. thick on knife edges which are 5 cms. `apart and whilst so supported by subjecting the test piece to a three point breaking load.

Results of such tests are shown in the following table which gives the breaking load in grams using different strength sols and differing penetrations.

Proportion of thickness penetrated Percent solids in sol M Breaking load untreated material 110 gms.

The heat insultation material produced as .above set forth has many uses.

` One important use if for lining a launder that is to be used to convey molten metal in a foundry. The launder may =be as shown in FIG. 2 and comprises a channel 14 defined by a support structure having an outer steel casing 15, a thickness 16 of vermiculite and ciment fondu, a thickness 17 of castable refractory material, the inner surface of which is lined by ya shaped blanket 18 for instance of the material of FIG. 1 positioned with its stitfened surface 19 to be in Contact with the flowing molten metal.

It is found that despite the fibrous nature of the material, the molten metal does not penetrate the treated surface or pick up fibres and also that problems due to frequent and large temperature changes are greatly reduced since cracks in the metal-contacting surface are avoided. Further if the surface is damaged it can be readily repaired.

I claim:

1. A method of producing heat-insulating material which comprises the steps of forming a felted or matted layer of material fibres incorporating alumina and silica, effecting controlled Istiffening of the layer by applying quantities of a silica sol to one surface of the layer to effect penetration of the silica sol from that surface a substantial distance only part way through the thickness of the material towards the other surface, the remaining thickness of the material being free of silica sol and being a substantial proportion of the thickness of the material, and heating the treated material at a temperature above 30 C. to dry the layer to stifen only the portion thereof into which the silica sol penetrates, the remaining portion free of silica sol being unstiffened.

2. A method according to claim 1, wherein the silica sol contains between 5% and 35% by weight of solids.

3. A method according to claim 1, wherein the silica sol contains between 9% and 21% by weight solids.

4. A method according to claim 1, wherein the silica sol contains between 9% and 11% solids.

5. A ceramic bre blanket layer of mineral fibres containing between 40% and 60% alumina and between 60% and 40% silica, said blanket layer having `a first, substantial, portion of its thickness extending from one surface towards its other surface stiffened by the application of silica sol and having a remaining, substantial, portion of its thickness extending from said first portion to said other surface untreated and resilient.

6. A molten metal conveying channel comprising a support structure and a heat-insulating channel lining with which the molten metal is in contact, said lining being a ceramic blanket layer as claimed in claim 5 fitted in said support structure with the stiffened first portion adjacent the metal liow.

References Cited UNITED STATES PATENTS 3,017,318 l/1962 Labino et al. 161-170 XR 3,023,141 2/1962 Hartwig 162-152 3,077,413 2/1963 Campbell 117-126 XR ROBERT F. BURNETT, Primary Examiner R. H. CRISS, Assistant Examiner U.S. C1. XR. 

